fwa_locatealonginterval details

[smnorris]

1. The index row counter for the features returned is 0 based. I am not sure why I did this, but I'd think 1 based makes more sense in the db context. This would change the behaviour of the web service output (and is unimportant), so I will leave as is.

2. The argument order would probably be better as (interval, start, end) vs (start, interval, end). Since arguments are named when calling the function via pgfs, this tweak should have no effect on existing users.

I'm considering these tweaks because I'm adding a new function FWA_SegementAlongInterval with very similar args (returning the line segments along the intervals, rather than the endpoints).